Draft tube



May 7, 1929. G.' A. JESSOP 1,711,891

DRAFT TUBE Filed March 11, 1925 3 Smeets-sheet 1 w b. .N

f X m\ WY# PN G. A. JESSOP May 7', 1929.

' DRAFT TUBE F11ed Mami 11, 1925 5 Sheets-Sheet May 7, 1929. G. A. JEssoP 1,711,891

DRAFT TUBE filed March 11, 1925 *5 sheets-sheet 3 nuento/o Patented May 7, 1929.

UNITED STATES 1,711,891 PATENT OFFICE.

. GEORGE A. JEssoP, OE YORK, PENNSYLVANIA, AssIGNoR To s. MORGAN SMITH COM- PANY, OE YORK, PENNSYLVANIA, A CORPORATION or PENNSYLVANIAE DRAFT TUBE.

Application led March 11, 1925, Serial No. 14,850.

This invention relates to draft tubes and particularly to the elbow type formed of concrete or other analogous material, or metal. n v,

Draft tube structures at presentiinvolve many important features that require careful consideration and analysis to meet and Satisfy contingencies and demands of various installations in ordery to maintain the greatest efficiency possible in the operation of turbines and other analogous water power mechanisms, not only in primary placements but also in repair or replacement work. For various well known Vreasons, therunner orwater wheel of a turbine or analogous powerinstallation is practically always set at some distance above normal tail water elevation, and itis necessary to have a draft tube in order to make use of the head between the wheel and tail water.

The velocity out. of the runner is compara- Y tively high and therefore the energy of the water at thispoint is considerable. In general Vthe `function ofV anyfdraftV tube is to make use of the static head between the Vrunner or water wheel Vand the tail race and also to regain the velocity head at the vdischarge end of the runner by gradually, lsmoothlyV and efficiently converting this large velocity head into pressure head, so. that it can become effective upon the runner or wheel itself. The effect of this vchange from velocity `head to pressure head is to decrease thev back pressure under therunner or wheel.. The conversion kof-velocity head into pressure head must be'done as eiiicientlyl as possible, and in order to accomplish this desirable result, itis necessary. that the rapidly moving waterv in thedraft tube'remain in full 'flowing contactl with the sur-v faces-of the tube at all points. ln an elbow draftltube it is very difficult to keep the water in full flowing contact with thedownstream or upper face of. the tube where the turn is made from the vertical to the horizontal, and ifA this contact of ythe water with.r

The primary and :most essential v,Object of thepresent invention, therefore, isfto sodcon-Qf, a struct draft' tube'that the Water-mtl bfi i ystruction thereof.

scribed andclaimed.

ymaintained in full flowing contactwith all surfaces of the draft tube and particularly the downstream or upper face of the tube where the turn or elbow is formed without inthe least detracting from the desirable eiiciency of operation. This water contact with all surfacesV of the tube is accomplished through the medium of structural features which'will be hereinafter specified. l

Further objects of the invention a-rerto generally improve draft tube structures and obtain an eiiicient device of this class without requiring an undue amount of excavation either in depth or width; to so ,construct a draft tube that, if desired, the center line of the runner or wheel ycan be placed close to -tail water; and thus decrease the requiredy ypossible and thereby minimize the expenditurevof time andcost inthe lay-out and con- The inventionconsists essentially inproviding adraft Atube having an elbow the upstream and downstream surfaces of which are so-curved as to maintainthe water in full contact therewith, and'also in providing such a draft tube which is gradually de# creased in transverse vertical extentor 'breadth froml a predetermined po-int above and fullythroughthe turn or elbow, and increasedin lateral or horizontal. extent, and gradually widened towards the outlet eX- tremity, a gradual increase in cross-Sectional area from the upper inlet to the lower outylet'- extremity being regularly maintained. lTheinvention ,furtherl consists in the general constructionand arrangementA of parts lwhich will. belkmore fully hereinafter def The accompanying drawingsillustratefthe y improved draftl tube formedv ofV concrete or analogous cementitious material, but it will 'be/understoodthat the Sam@ eavntal feasection on the line section on the line section on the line section on the line Fig. 7 is a transverse section on the line 7 7, Fig. 1.

Fig. 8 is a transverse section on the line 8*-8, Fig. 1.

Fig. 9 is a vertical section onthe line 9 9, Fig. 1. i

The numeral 5 designates a concrete or other cemeiititious structure in which the improved draft tube is suitably formed, the latter comprising an upper inlet extremity 6 over which the runner or wheel is adapted to be mounted in the usual manner. The

concrete or other analogous structure 5 mayv be continued upwardly any suitable distance to serve as a base support for the installation of the remaining part of a turbine orV other water power organization, and also for the purpose of rsupporting a power house in which the turbine unit or units are disposed. The upper member 7 of the improved ydraft tube is shown as composed of sheet or other metal down to the point 8, the remaining part of the draft tube being shaped in the concrete or other material 5. It will be understood, however, that the upper member 7 of the draft tube, which may be specified thev inlet member, may in some instances be constructed or shaped in the concrete.

@This upper inlet member 7 to a point-a short distance below the plane of section 2 2 is concentric with relation to an axial line 9, which is also the axis of the runnei' or wheel and the turbine shaft above. The upper inlet member 7 regularly flares in a downward direction. At a comparatively short distance below the plane of section 2 2 and as indicated by the plane of section 3 3, Fig. 3, the draft tube begins to assume an elliptical contour,k and this configuration increases graduallythrougli the elbow 10, as indicated by Figs. 4 to 9, inclusive7 respectively taken on the planes or' lines of section 4 4, 5 5, 6 6, 7 7, 8 8 and 9 9. In order to arriveat this construction, the curve 11 ofl the upstream or lower side of therelbow 10 isbegun prior to the curve 12 of the downstream or forward upper wall of the draft tube elbow. The rear or upstream curve 11 comes is also slightly bowled andV from the vertical to the horizontal in an are with a practically constant radius, or, in other words, with a constant curvature. The curvature 12 of the downstream or upper face of the elbow starts at a materially lower' elevation than the said upstream curve 11 when considering a vertical tube 'construction only. In other words, the curvature 12 of the downstream face of the elbow in the downstream direction starts much later than the curvature 11 of the upstream face. This downstream curve 12 of the upper face is an easement curve, that is, at the beginning thereofthere is a long radius of curvature and this radius is gradually decreased and becomesy a minimum at or near the end of the curve, as at 13, and which in a vertical setting is at the horizontal. .The diagram in Figure 1 shows the preferred manner of forming the easement curve, 01 r1, 02 7"-,`

OIL-a, @4 7, as r, OG WG, and 0?' 717 representing the radii of the` easement curve at the cross sections represented by the section lines 3 3, 4 4, 5 5, 6 6, 7 7, 8 8 and 9 9, and L representingthe locus of the centers of the various radii.V Taking the' lengths of the radii as shown in this dia-V gram, it will be seen that they decrease in length as they proceed from the section line 3 3 to the sectioiiline '9 9 and when the section line 9 9 is reached, the easement curve 12 has reached the horizontal andV hence the curvature is stopped at this point. This easement curve which, for the purposes of illustration, begins at or about the part of the draft tube elbow cut by the section line 3 3 and terminates at the point 13, is valuable and necessary in order to allow and assist the water to remain in full flowing' contact with the downstream or upper face of the elbow portion of thev draft tube, and thereby assist in maintaining a practically constantvelocity of water at a given section of the draft tube. The maintenance of a constant velocity at all points in a given lll* vtaken approximately at right angles to the longitudinal center line, is necessary in order to maintain smooth flow and therefore high efficiency in the tube. Again, for the purpose of illustration, let it be assumed thaty the tube is divided into three distinct parts. Therirst part is the vertical section or inlet member 7 with a straight vertical center line immediately below the runner. The sections at this inlet part or member of the tube are true, or approximately true, circles, and for convenience of description, the words breadth and width will be applied to the different sections of the tube, the breadth being intended to. mean the distance between the walls of the tube as cut by a plane passing through the longitudinal center line thereof, and by width is meant the distance between the walls of the tube as measured at right angles to the foregoing plane, each measurement passing through the longitudinal center line of the tube.

The second part of the tube is the curved or elbow section l0. The breadth of the tube is a maximum at the end of the first part, and at the beginning of the second part or section or elbow 10. lThe breadth of the first part or inlet member 7 relatively decreases from its maximum at the entrance of this second part or section to4 its minimum at or near the end of the bend or elbow as at 13. In other words, the yupstream or lower face of the draft tube defined by the curve l1 approaches and gets nearer to the downstream or upper face of the draft tube defined by the curve'lQ. At thesame time the width of the draft tube isl increased all along the bend or elbow, and this increase is such that the area of the tube is constantly increasing, so that the velocity ofv the water in the tube is constantly decreasing, or the velocity head is constantly being converted into pressure head. The reduction 4in the breadth of the tube from the beginning of the upper end of the second section or part or elbow lOis accomplished by making the curvature of the upstream and downstream faces of the tube, or the lower and upper sides of the tube, in the curvature forms hereinbefore specified andalso because the curvature of the downstream or upper face or side is' started at'a considerably-lower point or later than the curvature of the upstream face.

The third part or section of the tube is the horizontal lleg l5. Both t-he breadthv and.

width of this leg can increase gradually, and it is not necessary that both increase, -in view of the fact that one, for instance the breadth or vertical extent of thel'leg, could remain consant and even be decreased, provided the width or lateral extend of the tubo be. increased a sufficient degree sowas to maintain the constantly increasing area as theV water approaches nearer and nearer the outlet 16; As hereinbefore indicated, from the entrance off the improved tube to vthe outlet thereof the area is constantly increasing and therefore the velocityof the water is constantly decreasing. c Y

By lthe term easement curve as hereinbefore referred to, is to be understood the well known engineering definition and which is a curve usually introducedA between a tangent and a circular curve, and isv a curve of varying radius, which leaves the tangent as a very flat curve and grows sharper and Y sharper until it has the same radius Vas the circular curve, but in the'present improved draft tube, instead of the curve terminating in av circular curve, it ends inv nearlyV a straight tangent to the curve, as the bottom 40f the curve, 01g he end .of Vthev elbows, is, reached. f

* Theoperation of the improved draft tube is very simple.' The water entering the inlet member from the runner passes down into the bend. or f elbow which is reduced in breadthfrom the upstream towardsA` the downstream portion thereof and increased in width or lateral extent, and upon reaching the elbow the water is guided forward or towards the downstream portion or side of the elbow bend and at the same time spreads laterally yor in a horizontal direction and continues on through the outlet extremity of vthe leg and is finally discharged from the The construction of the elbow bend l latter. 'as specified'eliminates objectionable whirls or eddies' and causes the draft tube throughout its length to be filled, full flowing, with Vthe water discharged from the runner or vertical tothe horizontal inl'an arcfwith a' practically constant radius and the opposite 'or downstream portionhaving an easement curvebeginning with a long radius or curvature which gradually decreasesv and becomesl a minimum at or near the end of the curve, to decrease the breadth of the-elbow bend in a direction from the 'upstream' towards the ldownstream fportion of the tube, the tube having an increasefin'width or lateral ex tent at the elbow which increase in width is at least equal, in proportion tothe area, to said ydecrease in breadth.

v 2. An elbow draft tube comprising inlet and outlet extremities with an elbow kbend between'and continuous therewith, the inlet extremity being concentric withrelation to a central axis and the rear or upstream por- 'tion'of thektube formed rby4 a curve' that comes from the vertical to the horizontal' in an arc with a practically constant radius, the downstream portion of the elbowbend an easement curve which starts with a long radius of-curvature that gradually decreases and` becomes a minimum at thel end ofthe curve.` f i A drafttube having an inlet extremity "concentric with relation to a central laxis and continuing into an elbow whichis grad-k l ually decreased in breadth from the'upthereofby means V"of an upstream, prac- `stream towards the downstream portion stream easement curve, the tube being laterally increased in width and terminating in an outlet extremity.

4. A draft tube having an inlet extremity concentric with relation to a` central axis and continuing into an elbow which is gradually decreased in breadth from the upstream towards the downstream portion thereof by means of an upstream, practically constant radius curve and a downstream V easement curve and proportionately laterally increased in width and terminating in an outlet leg, the draft tube from its inlet yto it-s outlet extremity increasing in area.

5. A draft tube comprising an inlet member and an outlet leg with an elbow bend therebetween, the said elbow bend being decreased in breadth from the upstream towards the downstream portion thereof by means of any upstream, practically constant vradius curve and a downstream easement tent and continued with this lateral increase through the elbow bend in a direction from the upstream towards the downstream portion. of said bend, the elbow bend having an upstream, practically constant radius curve and a downstream easement curve.

7. A draft tube having inlet and outlet extremities wit-h an elbow bend therebetween and gradually increased in lateral extent from the inlet extremity, which is circular, to the outlet at a material distance beyond the termination of the elbow bend, the elbow bend correspondingly and gradually increasingr in lateral extent throughout the format-ion thereof towards the outlet extremity, the elbow bend having an upstream, practically constant radius curve and a downstream easement curve.

8. A draft tube having inlet and outlet extremities with an elbow bend interposed between said extremities and continuous therewith, the said elbow bend being materially flattened in a transversevertical direction within the area of the bend from the upstream towards t-he downstream portion thereof and also increased in width within the area of the. bend towards and regularly continuing into the outlet extremity, the elbow bend having an upstream, practically constant radius curve and a downstream easement curve.

9. A draft tube having inlet and outlet i extremities and anelbow'bend between the two extremities, the inletV extremity being concentric with relation to. a central axis and regularly continuing into the elbow bend, the elbow bend decidedly decreasing in breadth by an upstream, practically constant radius curve and a downstream easement curve, the bend also positively increasing in width divergently and this divergence regularly and fully continuing to the outlet extremity of the tube.

10. A draft tube having an inlet extremity concentric with relation to a central axis and continuing into an elbow which is gradually decreased in breadth from the upstream towards the downstream portion thereof by an upstream, practicallyconstant radius curve and t a. downstream easement curve, the draft tube being increased `in width and terminating in an outlet extremkity having a-fiattened top portion.

' 11. A draft tube having an inlet extremity concentric with relation to a central axis and continuing into an elbow which is gradually decreased in breadth from the upstream towards the downstream portion thereof by means of an upstream, practically constant radius curve and a downstream easement curve and proportionately laterally increased in width andterminating in an outlet leg, the said out-let leg having a flattened top portion and opposite vertical sides, the

ydraft tube from its inlet to its outlet extremity increasing in area.

l2. A draft tube having inlet and outlet extremities with an elbow therebetween, the elbow bend having an upstream substantially constant radius curve and a downstream easement curve.

13. An elbow draftv tube having an inlet extremity concentric with lrelation to a central axis and Vwherein also the elbow bend has an upstream substantially constant radius curve and a downstream easement curve.

14. A draft tube havingacircular inlet, an elbow bend contracted inbreadth and expanded in width and continuous with the said inlet and operating to cause a round column of water entering the draft tube ahead of the elbow bend to be flattened in breadth and expanded .in width, the velbow lthereof byy an upstream, practically constant radiuscurve and a downstream easement curve, the draft tube being increased in width and terminating in an outlet extremity vhaving a flat upwardly flaring top portion.

16. A draft `tube having an inlet extremity concentric to a central axis and continuing into an elbow which is gradually detherebetween, the said elbow being decreased in breadth from the upstream towards the downstream portion thereof byv means of an upstream, practically constant radius curve and a downstream easement curve, said easement curve starting at a materially lower elevation than said constant radius curve, and thev said elbow bend being correspondingly and proportionately increased in width, the outlet leg having a flattened top portion with an upward flare, the top portion being straight in a transverse direction.

18. A draft tube having inlet and outlet Y extremities with an elbow bend therebetween and gradually increased in lateral extent from the inlet extremity which is circular in contour to theA outlet leg ata distance beyond the termination of the elbow bend, the elbow bend correspondingly and gradually increasing in lateral extent throughout the t' formation thereof towards the outlet extremity, the elbow bend having an upstream, i

practically constant radius curve and a downstream easement curve, the elbow also gradually decreasing in vertical extent towards the outlet extremity, and the outlet extremity having a flattened top which is transversely straight from side to side, and continues with diminishing structure partially into the downstreamL side of the elbow and also flares upwardly towards the terminal of the outlet extremity from the elbow.

19. A draft tube having inlet and outlet extremities and an elbow bend between the said extremities, said elbow bend at the upstream portion having a curve which comes from the verticalto the horizontal in an arc of a circle and the opposite or downstream portion having an easement curve which is formed in the center with a dip towards and merging into the top of the outlet extremity and providing an 'easement curve with less rapid change of curvature at its terminal and which merges into the outlet extremity which has a transversely straight flattened top, the outlet extremity being proportionately increased in width with relation to the remaining part of the tube and the outlet extremity having a gradual upward flare from the elbow bend to the end of said outlet extremity.

20. A draft tube having an inlet extremity concentric with relation to a central axis and continuing into an elbow which is gradually decreased in breadth from the upstream towards the downstream portion thereof by anA upstream practically constant radius curve and a downstream easement curve, the draft tube being increased in width and terminating in an outlet extremity having a flattened bottom portion.

21. A draft tube having an inlet extremity substantially concentric with a central axis and continuing into an elbow which gradually decreases in breadth from the upstream towards the downstream portion thereof by means of an upstream practically constant my hand.

. GEORGE A. JESSOP. 

